1. Field of the Invention
The present invention relates to a frame of a press-dehydrating section in a paper making machine.
2. Description of the Prior Art
First, a general construction of a press-dehydrating section in a paper making machine in the prior art will be described with reference to FIGS. 6 and 7. As shown in these figures, in the press-dehydrating section, a wet paper web (fiber mat) 1, which has been dehydrated to a concentration of about 15-18% in the upstream wet end section and is fed thereto, is further dehydrated by making it successively pass through gaps between a plurality of pairs of press rolls, and is then fed to the downstream heat-dry section. The fiber mat 1 is fed in the downstream section with the aid of a wire 24, that is, an endless net belt which is wound around a plurality of rolls and travels in the direction of the arrow by a roll 25 rotated by a driving device not shown. The web is transferred into the press-dehydrating section by a sucking force of a suction roll rotatably provided at an inlet section of the apparatus. The fiber mat 1 thus transferred in is dehydrated by a pinching action of a press roll 28 and a suction roll 29 in a first press section 27, and is wound around the suction roll 29 to travel to the next press section. Subsequently, predetermined dehydration is effected as passing the web through a second press section 30, a third press section 31 and a fourth press section 32 each having a similar capability, and then the fiber mat 1 is carried out towards the heat-dry section.
In the above-described first to fourth press sections, one of the paired press rolls has its opposite axial ends pivotably supported by a bracket 33, and this bracket 33 is fixedly secured to a swing arm 34 that is supported rotatably about a shaft 35 and adapted to be rocked via a cylinder 18. Accordingly, if the above-mentioned cylinder 18 is actuated via an electromagnetic valve (not shown), then a pressing force can be generated between the paired rolls, but if the cylinder 18 is actuated in the opposite direction, a gap can be formed between the respective rolls. In addition, if the pressure applied to the cylinder 18 is made variable, then the pressing force generated between the rolls can be arbitrarily controlled, so that at the respective press sections and the dehydrating rates can be controlled in a sensitive manner. It is to be noted that in FIG. 7, reference numeral 15 designates endless felts, which are wound around a plurality of rolls and travel in synchronism with the fiber mat 1 by a driving device (not shown), and which have functions of facilitating the desired dehydrating effect and serving as a guide for conveyance.
As described above, in the press-dehydrating section, dehydration of the fiber mat 1 is effected by a strong pressing force between press rolls, and so, it is necessary to cause a considerably strong roll pressure to be generated between the paired rolls. Accordingly, the shaft 35 serving as a fulcrum for the above-described swing arm 34 must have a mechanical strength that is high enough to sufficiently withstand the reaction force against the above-mentioned pressing force, and the frame forming a framework of the apparatus must also have a corresponding mechanical strength. To that end, it is a common practice to at the opposite side edge portions of the top of the apparatus, employ fixed frames (top beams) 2 extending along the direction of travel of the fiber mat 1 so that the apparatus may have a mechanical strength that is high enough to sufficiently withstand the above-mentioned reaction force.
Now the procedure of replacing a press roll will be described. Among the press rolls, there are many varieties of rolls corresponding to desired functions such as rolls 16 and 17 having their surfaces coated with rubber, a suction roll having a hollow inner space and a plurality of air-permeable holes in its circumferential wall, a press roll 8 made of different material, or the like, and hence, during a long period of use, wear and damage arises, which necessitates predetermined repairs. Especially in the case of a rubber roll, in view of its structural characteristic, regrinding of its surface becomes necessary due to wear and the like, and normally it is a common practice to replace the roll every three to six months or more.
And replacement of such a roll is carried out by performing the steps of displacing a roll, positioned right above the roll to be replaced, backwards or forwards in the traveling direction of the fiber mat 1 to a predetermined position, disconnecting a shaft coupling of the roll to be replaced and a press member for a bearing housing 20 (See FIG. 5) pivotably supporting the same roll, hanging the roll with a hoist provided on a ceiling, further transferring it in the axial direction towards the operation side [throughout this specification, the term "operation side" is used to refer to the side faced to a passage of a worker along the traveling direction of the fiber mat (sometimes it is also referred to as "front side"), and the term "drive side" is used to refer to the side opposite to the above-mentioned "operation side" (sometimes it is also referred to as the "rear side")], thereby transferring the roll to a predetermined position.
The process of hanging and carrying a roll out of the device in the prior art is illustrated in FIGS. 5(a) to 5(d), in which a 2-crab 3-hook type of hoist was used. This type of hoist operates by making use of two sets of hanging units consisting of a hanging unit 37 provided with a single hook 21 and a hanging unit 38 provided with two hooks 36 and 22. At first, wires 23 wound around the outside end portions of a roll shaft are hung from the hooks 21 and 22 at the opposite outer ends and are moved in the axial direction of the roll under the raised condition as shown in FIGS. 5(a) and 8(a), and are stopped at the position shown in FIG. 8(b). Subsequently, a nylon sling 39 wound around the outer circumference of the roll is hung from the hook 36 as shown in FIGS. 5(b) and 8(c), then the hook 22 positioned at the end of the roll on the side of the drive machine is lowered, and the wire 23 which was hung from the hook 22 is disengaged from the latter as shown in FIG. 5(c).
During the above-mentioned steps, the top frame 2 above the roll can be avoided, as the roll is moved in the axial direction to the position shown in FIGS. 5(c) and 8(d), and subsequently, the roll can be conveyed to a predetermined position. FIG. 5(d) illustrates the mode of transfer from the engagement of the roll with a wire 23 shown at (A) to the engagement thereof with a nylon sling 39 shown at (B). It will be obvious that to assemble a new roll, steps in a sequence reverse to those described above are effected. As described above, the replacement of the roll in the prior art difficult, dangerous and time-consuming requiring such steps as rehanging a roll midway during the process of carrying the roll out of the device, in view of interference with a frame structure.
In addition, as an improved frame structure for allowing another method of effecting replacement of a roll in a simple and safe manner by obviating the rehanging step, a frame structure that is advantageous for allowing the replacement of a roll is disclosed in U.S. Pat. No. 4,608,128 (See FIG. 9). However, according to this method, intermediate frame members (connection blocks) 65 are required on both the operation side and the drive side, and moreover, for the purpose of allowing the replacement of a roll, the connection blocks on both sides must be manipulated to be moved. Also, despite the fact that, for the purpose of allowing the replacement of a roll, it is only necessary to ensure a space for allowing a rope to pass therethrough at least only on the operation side, unnecessary work, that is, the dismounting of the block on the drive side and mounting the same is required, and so the procedure for replacement is increased by one step. Moreover, besides the pressing device for a roll, means 64 for revolving a roll is required on both the operation side and the drive side, and so, an increase in the cost of a machine caused by an increase in the number of machine parts is brought about.
During the replacement of a roll in the above-described frame structure of a press-dehydrating apparatus in a paper making machine in the prior art, since a movement of wires 23 is necessary for hanging and carrying a roll out of the frame structure is limited by a frame (top beam) 2 fixedly extending along the direction of travel of a fiber mat at the opposite side edge portions of the top of the above-described press-dehydrating apparatus, inevitably the operation of rehanging a roll with the aid of an additional hook 36 in the middle of carrying the roll out of the frame was effected, as a counter-measure for avoiding the same frame 2. Moreover, there were problems such that the above-described operation of rehanging a roll which is heavy was very dangerous, and that due to this rehanging step, a relatively long time was necessary for the replacement of a roll.